European party systems have undergone some fundamental changes in recent decades. The historic dominance of Christian Democratic, Socialist and Liberal parties has been challenged by new, often “populist” parties from both right and left, some of which have even become parties of government. The underlying sources of this transformation are the subject of sustained scholarly attention. Some analysts see major social transitions as the cause, as secularization and economic forces erode the traditional constituencies of previously dominant parties. Other scholars argue that generational changes in social values, variously defined, are the impetus for new political alignments. These values are made salient by contemporary issues confronting the continent, such as climate change, immigration, changing family structures, or the war in Ukraine. Finally, many observers claim that divisions between transnationalists and nationalists, epitomized by debates over the role of the European Union, are adding a new dimension to party divisions. We find that historic religious and social class divisions still shape party alignments, albeit in some new ways, as does the traditional left-right ideological divide, supplemented by new issues often associated with theories of value change. We show that these factors also help explain the oft-noted political “fragmentation” of the EU parliament, as the eight groups differ in crucial characteristics.